package org.pr.springboot_autodev.util;

/**
 * @ProjectName: SpringBoot_AutoDev
 * @Package: org.pr.springboot_autodev.util
 * @ClassName: SnowflakeIdWorker
 * @Author: LXC
 * @Description: 雪花算法
 * @Date: 2025/8/28 23:15
 */
public class SnowflakeIdWorker {
    // 起始时间戳 (2020-01-01)
    private final long twepoch = 1577836800000L;

    private final long workerIdBits = 5L;      // 机器 ID 所占位数
    private final long datacenterIdBits = 5L;  // 数据中心 ID 所占位数
    private final long sequenceBits = 12L;     // 序列号所占位数

    private final long maxWorkerId = ~(-1L << workerIdBits);
    private final long maxDatacenterId = ~(-1L << datacenterIdBits);
    private final long sequenceMask = ~(-1L << sequenceBits);

    private final long workerIdShift = sequenceBits;
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    private long workerId;
    private long datacenterId;
    private long sequence = 0L;
    private long lastTimestamp = -1L;

    public SnowflakeIdWorker(long workerId, long datacenterId) {
        if (workerId > maxWorkerId || workerId < 0)
            throw new IllegalArgumentException("worker Id out of range");
        if (datacenterId > maxDatacenterId || datacenterId < 0)
            throw new IllegalArgumentException("datacenter Id out of range");
        this.workerId = workerId;
        this.datacenterId = datacenterId;
    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            throw new RuntimeException("Clock moved backwards. Refusing to generate id");
        }

        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        return ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift)
                | (workerId << workerIdShift)
                | sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }
}
